1. Field of the Invention
The invention relates to a fuel injection valve for internal combustion engines, of the kind used for injecting fuel into the combustion chamber of an internal combustion engine.
2. Description of the Prior Art
Fuel injection valves, of the kind preferably used for injecting fuel directly into the combustion chamber of an internal combustion engine, have long been known from the prior art. In injection systems that operate on the so-called common rail principle, fuel compressed by means of a high-pressure pump is made available in a so-called rail and injected by means of injectors into the various combustion chambers of an internal combustion engine. The injection is triggered by means of a nozzle needle, which executes a longitudinal motion and thereby opens and closes one or more injection openings. Since in the injection of fuel at high pressure, in particular, it is not sensible or is impossible to move the nozzle needle directly by means of an electrical actuator, hydraulic forces that the compressed fuel exerts on the nozzle needle are employed for the triggering. For that purpose, a control chamber is embodied in the fuel injection valve, and the force of the control chamber acts directly or indirectly on the nozzle needle and presses it thereby against a nozzle seat, so that the nozzle needle closes the injection openings. By varying the pressure in the control chamber and thus the closing force on the nozzle needle, the longitudinal motion of the nozzle needle can be controlled in a purposeful way.
The fuel pressure in the control chamber is varied by means of a control valve; the control chamber is made to communicate in alternation with a leak fuel chamber, in which a low pressure prevails, or this communication is interrupted by means of the control valve. From German Patent Disclosure DE 10 2004 030 445 A1, a fuel injection valve is known which has a control valve of this kind. The control valve is embodied there as a so-called 3/2-way valve, and it controls the communication of the control chamber on the one hand with the high-pressure source, from which the compressed fuel is delivered to the injection valve, and on the other to a leak fuel chamber that has low pressure. The control valve has a control valve member, which can be moved inside the control valve chamber by means of an electrical actuator, such as a magnet or piezoelectric actuator, and thus cooperates with a first control valve seat and a second control valve seat. If the control valve member is in contact with the first control valve seat, then the communication of the control valve chamber with the leak fuel chamber or to a leak fuel connection that has a communication with a low-pressure region is closed. Since both the outlet throttle restriction, which from the control chamber of the nozzle needle discharges into the control valve chamber, and the bypass throttle restriction, which connects the high-pressure conduit to the control conduit, open into the control valve chamber, the result is communication of the high-pressure conduit with the control chamber via the outlet throttle restriction.
If the pressure is to be lowered in the control chamber, then by means of the electrical actuator the control valve member is moved away from the first control valve seat into contact with the second control valve seat. As a result, the communication of the control valve chamber with the leak fuel chamber is opened, while simultaneously the bypass throttle restriction, which connects the high-pressure conduit with the control valve chamber, is closed. The resultant communication of the outlet throttle restriction from the control chamber with the leak fuel chamber via the control valve chamber leads to an outflow of the fuel pressure in the control chamber and thus to a corresponding pressure reduction, which leads to a lowering of the closing pressure on the nozzle needle and finally to a motion of the nozzle needle away from the nozzle seat and for opening the injection openings.
A control valve that functions quite similarly is further known from International Patent Disclosure WO 2006/067015 A1, which functions essentially in the same way. Once again, the control valve member is surrounded by the fuel pressure of the control valve chamber and thus is acted upon on all sides by the fuel pressure of the control valve chamber. The control valve functions as described above, in such a way that initially, the control valve member is in contact with the first control valve seat and is moved by an electrical actuator into the control valve chamber, until it is in contact with the second control valve seat. The control valve member has to be moved away from the first control valve seat counter to the fuel pressure in the control valve chamber. Since initially, at least approximately the same pressure as in the control chamber of the nozzle needle prevails in the control valve chamber, and this pressure in turn is approximately equivalent to the fuel high pressure supplied, this force is quite strong, so that a suitably powerful actuator with suitably high capacity is a prerequisite.
Moreover, the known control valves have the disadvantage that the control valve member is prestressed toward the first control valve seat by a strong spring. This is necessary to ensure reliable closure of the control valve even whenever the hydraulic forces on the control valve member vary sharply because of the motion of the control valve member in the control valve chamber. However, a very strong closing spring has the disadvantage that the control valve member, even at relatively slight injection pressures, or in other words whenever only a slight fuel pressure prevails in the control valve chamber, is pressed against the first control valve seat by the very strong spring. The result is unnecessarily high wear at the first control valve seat, which can adversely affect the service life of the fuel injection valve.